Kinetic Modeling of the Autohydrolysis of Lignocellulosic Biomass for the Production of Hemicellulose-Derived Oligosaccharides

Potential of Wood Hemicelluloses and Their Derivates as Food Ingredients

A holistic utilization of all lignocellulosic wood biomass, instead of the current approach of using only the cellulose fraction, is crucial for the efficient, ecological, and economical use of the forest resources. Use of wood constituents in the food and feed sector is a potential way of promoting the global economy. However, industrially established food products utilizing such components are still scarce, with the exception of cellulose derivatives. Hemicelluloses that include xylans and mannans are major constituents of wood. The wood hemicelluloses are structurally similar to hemicelluloses from crops, which are included in our diet, for example, as a part of dietary fibers. Hence, structurally similar wood hemicelluloses have the potential for similar uses. We review the current status and future potential of wood hemicelluloses as food ingredients. We include an inventory of the extraction routes of wood hemicelluloses, their physicochemical properties, and some of their gastrointestinal characteristics, and we also consider the regulatory route that research findings need to follow to be approved for food solutions, as well as the current status of the wood hemicellulose applications on that route.

Effects of Hydrothermal Processing on Miscanthus × giganteus Polysaccharides: A Kinetic Assessment

Miscanthus × giganteus samples were characterized for composition and treated with hot compressed water (hydrothermal or autohydrolysis treatments) at temperatures in the range of 190-240 °C. The liquid phases from treatments were analyzed to assess the breakdown of susceptible polysaccharides into a scope of soluble intermediates and reaction products. The experimental concentration profiles determined for the target compounds (monosaccharides, higher saccharides, acetic acid and sugar-decomposition products) were interpreted using a pseudohomogeneous kinetic mechanism involving 27 reactions, which were governed by kinetic coefficients showing an Arrhenius-type temperature dependence. The corresponding activation energies were calculated and compared with data from the literature. The kinetic equations allowed a quantitative assessment of the experimental results, providing key information for process simulation and evaluation.

Recent progress in direct production of furfural from lignocellulosic residues and hemicellulose

Furfural is a vital biomass-derived platform molecule, which can be used to synthesize a wide range of value-added chemicals. Furfural and its derivatives are promising alternatives to conventional petroleum chemicals. However, recent industrial production of furfural existed some thorny problems, including low efficiency, energy waste, and environmental pollution. Therefore, tremendous and continuous efforts have been made by researchers to develop novel furfural production processes with high economic viability, production efficiency, and sustainability. This review summarized the merits and shortcomings of disparate catalytic systems for the synthesis of furfural from biomass and biomass pretreatment hydrolysate on the basis of recently published literature. Furthermore, the suggestions for furfural production research were put forward.

The Kinetics Studies on Hydrolysis of Hemicellulose

The kinetics studies is of great importance for the understanding of the mechanism of hemicellulose pyrolysis and expanding the applications of hemicellulose. In the past years, rapid progress has been paid on the kinetics studies of hemicellulose hydrolysis. In this article, we first introduced the hydrolysis of hemicelluloses via various strategies such as autohydrolysis, dilute acid hydrolysis, catalytic hydrolysis, and enzymatic hydrolysis. Then, the history of kinetic models during hemicellulose hydrolysis was summarized. Special attention was paid to the oligosaccharides as intermediates or substrates, acid as catalyst, and thermogravimetric as analyzer method during the hemicellulose hydrolysis. Furthermore, the problems and suggestions of kinetic models during hemicellulose hydrolysis was provided. It expected that this article will favor the understanding of the mechanism of hemicellulose pyrolysis.

Liquid Hot Water Pretreatment of Lignocellulosic Biomass at Lab and Pilot Scale

Liquid hot water pretreatment is considered to be a promising method for increasing biomass digestibility due to the moderate operational conditions without chemical additions. A necessary step towards the scalability of this pretreatment process is performing pilot plant trials. Upscaling was evaluated with a scaling factor of 500, by using 50 mL in the laboratory and 25 L in a pilot plant batch reactor. Pretreatment times were varied from 30 to 240 min, and temperatures used were 180–188 °C, while applying similar heating profiles at both scales. The initial mass fraction of poplar wood chips ranged from 10% to 16%. Liquid hot water pretreatment at laboratory and pilot scale led to analogous results. The acetic acid analysis of the liquid and solid fractions obtained after pretreatment indicated that complete deacetylation of poplar biomass can be achieved.

Controlling autohydrolysis conditions to produce xylan-derived fibers that modulate gut microbiota responses and metabolic outputs

Autohydrolysis is used for producing xylan-derived oligosaccharides from lignocellulosic biomass. Although numerous studies report optimized autohydrolysis conditions for various plants, few of these studies correlate process parameters with the resulting structural properties to their impact on intestinal bacterial communities. Thus, to further clarify these relationships, beechwood xylan (BWX)-derived substrates, processed under five conditions, were fermented in vitro by human gut microbiota. Autohydrolysis reduced the mean molecular size and substitutions of BWX. Distinct fermentation kinetics were observed with differing processing of BWX substrates, which correlated with impacts on community species evenness. The relative abundances of Bacteroides, Fusicatenibacter, Bifidobacterium, and Megasphaera within the fermentations varied with processing conditions. While the total short-chain fatty acid concentrations were the same among the treatments, processing conditions varied the extent of propionate and butyrate generation. Autolysis parameters may be an important tool for optimizing beneficial effects of xylan-derived fibers on human gut microbiota structure and function.

Two-stage processing for xylooligosaccharide recovery from rice by-products and evaluation of products: Promotion of lactic acid-producing bacterial growth and food application in a high-pressure process

In this study, we attempted to maximize arabinoxylan conversion into xylooligosaccharide (XOS) from rice husk and rice straw using two saccharification processes and evaluate the promotion of lactic acid-producing bacterial growth, including an investigation of the role of prebiotics in protecting probiotic bacteria in rice drink products in a high-pressure process (HPP). Hydrothermal treatment followed by enzymatic hydrolysis was designed for XOS recovery from rice husk arabinoxylan (RH-AX) and rice straw arabinoxylan (RS-AX). The hydrothermal treatment performed at 170 °C for 20 min and 180 °C for 10 min was the optimal condition to produce XOS liquor from rice husk and rice straw, respectively. Pentopan mono BG successfully recovered XOS from rice husk and rice straw residues at 50 °C, pH 5.5, an enzyme concentration of 50 U and 100 U/g substrate for 24 h. This design converted 92.17 and 88.34% (w/w) of initial RH-AX and RS-AX into saccharides, which comprised 64.01 and 59.52% of the XOS content, respectively. Rice husk xylooligosaccharide (RH-XOS) and rice straw xylooligosaccharide (RS-XOS) had degrees of polymerization ranging from 2 to 6 with some arabino-xylooligosaccharides. RH-XOS and RS-XOS were used to examine the promotion of the growth of lactic acid-producing bacteria strains in the presence of other prebiotics. RH-XOS and RS-XOS strongly promoted the growth of Lactobacillus sakei and Lactobacillus brevis, while other species showed weak to moderate growth. This study represents the first report of the powerful effect of Lactococcus lactis KA-FF1-4 on altering the utilization of XOS but not xylose. Furthermore, for the first time, we reported the capability of XOS to protect probiotics in rice drinks under high-pressure conditions. RH-XOS and RS-XOS resulted in the highest viability of approximately 11 log cfu/mL and exhibited no significant difference compared with the non-HPP treatment. Hence, rice husk and rice straw can be utilized as alternative prebiotic sources that provide biological activity and food applications in the HPP industry.

Friend or Foe? Impacts of Dietary Xylans, Xylooligosaccharides, and Xylanases on Intestinal Health and Growth Performance of Monogastric Animals

This paper discusses the structural difference and role of xylan, procedures involved in the production of xylooligosaccharides (XOS), and their implementation into animal feeds. Xylan is non-starch polysaccharides that share a β-(1-4)-linked xylopyranose backbone as a common feature. Due to the myriad of residues that can be substituted on the polymers within the xylan family, more anti-nutritional factors are associated with certain types of xylan than others. XOS are sugar oligomers extracted from xylan-containing lignocellulosic materials, such as crop residues, wood, and herbaceous biomass, that possess prebiotic effects. XOS can also be produced in the intestine of monogastric animals to some extent when exogenous enzymes, such as xylanase, are added to the feed. Xylanase supplementation is a common practice within both swine and poultry production to reduce intestinal viscosity and improve digestive utilization of nutrients. The efficacy of xylanase supplementation varies widely due a number of factors, one of which being the presence of xylanase inhibitors present in common feedstuffs. The use of prebiotics in animal feeding is gaining popularity as producers look to accelerate growth rate, enhance intestinal health, and improve other production parameters in an attempt to provide a safe and sustainable food product. Available research on the impact of xylan, XOS, as well as xylanase on the growth and health of swine and poultry, is also summarized. The response to xylanase supplementation in swine and poultry feeds is highly variable and whether the benefits are a result of nutrient release from NSP, reduction in digesta viscosity, production of short chain xylooligosaccharides or a combination of these is still in question. XOS supplementation seems to benefit both swine and poultry at various stages of production, as well as varying levels of XOS purity and degree of polymerization; however, further research is needed to elucidate the ideal dosage, purity, and degree of polymerization needed to confer benefits on intestinal health and performance in each respective species.

Xylanolytic Bacillus species for xylooligosaccharides production: a critical review

The capacity of different Bacillus species to produce large amounts of extracellular enzymes and ability to ferment various substrates at a wide range of pH and temperature has placed them among the most promising hosts for the industrial production of many improved and novel products. The global interest in prebiotics, for example, xylooligosaccharides (XOs) is ever increasing, rousing the quest for various forms with expanded productivity. This article provides an overview of xylanase producing bacilli, with more emphasis on their capacity to be used in the production of the XOs, followed by the purification strategies, characteristics and application of XOs from bacilli. The large-scale production of XOs is carried out from a number of xylan-rich lignocellulosic materials by chemical or enzymatic hydrolysis followed by purification through chromatography, vacuum evaporation, solvent extraction or membrane separation methods. Utilization of XOs in the production of functional products as food ingredients brings well-being to individuals by improving defense system and eliminating pathogens. In addition to the effects related to health, a variety of other biological impacts have also been discussed.

Unrevealing model compounds of soil conditioners impacts on the wheat straw autohydrolysis efficiency and enzymatic hydrolysis

BACKGROUND

Soil-derived exogenous ash (EA) poses a challenge toward lignocellulosic autohydrolysis due to its buffering capacity. Previous works focusing on this phenomenon have failed to also investigate the role that soluble salts, and organic matter plays in this system. Herein, sodium phosphate and sodium humate were employed as model buffering compounds representing soluble salts and organic matter and dosed into a de-ashed wheat straw (DWS) autohydrolysis process to show the potential impacts of WS attached soil conditioners on the WS autohydrolysis efficiency which would further affect the enzymatic digestibility of autohydrolyzed WS.

RESULTS

Results showed that with the increasing loadings of sodium phosphate and sodium humate resulted in elevated pH values (from 4.0 to 5.1 and from 4.1 to 4.7, respectively). Meanwhile, the reductions of xylan removal yields from ~ 84.3-61.4% to 72.3-53.0% by loading (1-30 g/L) sodium phosphate and sodium humate during WS autohydrolysis lead to a significant decrease of cellulose accessibilities which finally lead to a reduction of the enzymatic digestibility of autohydrolyzed WS from ~ 75.4-77.2% to 47.3-57.7%.

CONCLUSION

The existence of different types soil conditioner model compounds results in various component fractions from autohydrolyzed WS in the process of autohydrolysis. A lack of sufficient xylan removal was found to drive the significant decrease in enzymatic accessibility. The results demonstrated the various effects of two typical tested soil conditioners on WS autohydrolysis and enzymatic hydrolysis.

Preparation and characterizations of oil palm fronds cellulose nanocrystal (OPF-CNC) as reinforcing filler in epoxy-Zn rich coating for mild steel corrosion protection

Oil palm frond (OPF) is one of largest contributions to the biomass waste from oil palm plantation. In this work, OPF has been successfully utilized to prepare cellulose nanocrystal (OPF-CNC) by acid hydrolysis. OPF was initially treated with autohydrolysis treatment. The obtained OPF-CNC was characterized via complementary analyses. The produced OPF-CNC showed a high crystallinity index value (60%) and high BET surface area (26.10 m² g^-1) as compared to α-cellulose (crystallinity index: 54% and BET surface area:7.14 m²g^-1). The surface analyses via scanning electron microscope (SEM) and transmission electron microscopy (TEM) demonstrated that the OPF-CNC has a smooth surface with a needle-like shape, where the average length and diameter are 95.09 nm and 6.81 nm, respectively. The corrosion analyses via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) illustrate that the coated mild steel with the inclusion of 0.5 wt% OPF-CNC has managed to sharply reduce the corrosion (99%). The coated mild steel with the inclusion of 0.5 wt% OPF-CNC showed the highest hydrophobicity (100.5 ± 0.7°) and has lowest amount of O via water contact angle and energy dispersive X-ray spectroscopy (EDX) analyses respectively, indicating lowest corrosion rate.

Balancing the effect of pretreatment severity on hemicellulose extraction and pulping performance during auto-hydrolysis prior to kraft pulping of acacia wood

When using a combination of pre-extraction and chemical pulping, a high yield of sugar recovery and minimal negative effect on the subsequent pulping step are expected. In this work, the P factor was utilized to investigate the effect of auto-hydrolysis severity on sugar recovery, removal of the main component, and impact on the kraft pulping of acacia wood chips. Using a P factor of 235, 84.34% of the polysaccharides in 14.05 g L^-1 of dissolved sugars could be obtained. In addition, the soluble sugars were easily separated with a recovery yield of 3.54 g ·L^-1 and Mw of 4,690 g mol^-1 by direct precipitation using organic solvents. However, a maximum of 22.14 g L^-1 of dissolved sugars was obtained with approximately 72.53% polysaccharides and Mw of 2,198 g mol^-1 for a P factor of 601. Moreover, nearly 50% of the degraded carbohydrates remained in the auto-hydrolyzed wood chips. The decrease in the mass of pentosan, holocellulose, and klason lignin was 62, 30, and 8.76%, respectively. With intensifying severity, the screened yield and viscosity of pulps decreased markedly, whileas the Kappa number increased. No significant differences were observed in the morphology of the resultant fibers. Moreover, there was a decrease in the physical strength of the pulps due to the loss of the intrinsic strength of the pulp fibers, which in turn resulted from the cellulose damage. The combustion performance of the resultant pulping black liquor is improved due to the higher lignin content.

Toward Complete Utilization of Miscanthus in a Hot-Water Extraction-Based Biorefinery

Miscanthus (Miscanthus sp. Family: Poaceae) was hot-water extracted (two h, at 160 °C) at three scales: laboratory (Parr reactor, 300 cm3), intermediate (M/K digester, 4000 cm3), and pilot (65 ft3-digester, 1.841 × 106 cm3). Hot-water extracted miscanthus, hydrolyzate, and lignin recovered from hydrolyzate were characterized and evaluated for potential uses aiming at complete utilization of miscanthus. Effects of scale-up on digester yield, removal of hemicelluloses, deashing, delignification degree, lignin recovery and purity, and cellulose retention were studied. The scale-dependent results demonstrated that before implementation, hot-water extraction (HWE) should be evaluated on a scale larger than a laboratory scale. The production of energy-enriched fuel pellets from hot-water extracted miscanthus, especially in combination with recovered lignin is recommended, as energy of combustion increased gradually from native to hot-water extracted miscanthus to recovered lignin. The native and pilot-scale hot-water extracted miscanthus samples were also subjected to enzymatic hydrolysis using a cellulase-hemicellulase cocktail, to produce fermentable sugars. Hot-water extracted biomass released higher amount of glucose and xylose verifying benefits of HWE as an effective pretreatment for xylan-rich lignocellulosics. The recovered lignin was used to prepare a formaldehyde-free alternative to phenol-formaldehyde resins and as an antioxidant. Promising results were obtained for these lignin valorization pathways.

Low acid hydrothermal fractionation of Giant Miscanthus for production of xylose-rich hydrolysate and furfural

Low acid hydrothermal (LAH) fractionation was developed for the effective recovery of hemicellulosic sugar (mainly xylose) from Miscanthus sacchariflorus Goedae-Uksae 1 (M. GU-1). The xylose yield was maximized at 74.75% when the M. GU-1 was fractionated at 180°C and 0.3wt.% of sulfuric acid for 10min. At this condition, the hemicellulose (mainly xylan) degradation was 86.41%. The difference between xylan degradation and xylose recovery yield, i.e., xylan loss, was 11.66%, as indicated by the formation of decomposed products. The furfural, the value added biochemical product, was also obtained by 0.42g/L at this condition, which was 53.82% of furfural production yield based on the xylan loss. After then, the furfural production continued to increase to a maximum concentration of 1.87g/L, at which point the xylan loss corresponded to 25.87%.

Effects of Soluble Lignin on the Formic Acid-Catalyzed Formation of Furfural: A Case Study for the Upgrading of Hemicellulose

A comprehensive study is presented on the conversion of hemicellulose sugars in liquors obtained from the fractionation of Miscanthus, spruce bark, sawdust, and hemp by using formic acid. Experimental tests with varying temperature (130-170 °C), formic acid concentration (10-80 wt%), carbohydrate concentrations, and lignin separation were carried out, and experimental data were compared with predictions obtained by reaction kinetics developed in a previous study. The conversions of xylose and arabinose into furfural were inherently affected by the presence of polymeric soluble lignin, decreasing the maximum furfural yields observed experimentally by up to 24%. These results were also confirmed in synthetic mixtures of pentoses with Miscanthus and commercial alkali lignin. This observation was attributed to side reactions involving intermediate stable sugar species reacting with solubilized lignin during the conversion of xylose into furfural.

Simultaneous concentration and detoxification of lignocellulosic hydrolyzates by vacuum membrane distillation coupled with adsorption

Low sugar concentration and the presence of various inhibitors are the major challenges associated with lignocellulosic hydrolyzates as a fermentation broth. Vacuum membrane distillation (VMD) process can be used to concentrate sugars and remove inhibitors (furans) efficiently, but it's not desirable for the removal of less volatile inhibitors such as acetic acid. In this study, a VMD-adsorption process was proposed to improve the removal of acetic acid, achieving simultaneous concentration and detoxification of lignocellulosic hydrolyzates by one step process. Results showed that sugars were concentrated with high rejections (>98%) and little sugar loss (<2%), with the significant reduction in nearly total furans (99.7%) and acetic acid (83.5%) under optimal operation conditions. Fermentation results showed the ethanol production of hydrolyzates concentrated and detoxified using the VMD-adsorption method were approximately 10-fold greater than from untreated hydrolyzates.

Effect of structural changes of lignin during the autohydrolysis and organosolv pretreatment on Eucommia ulmoides Oliver for an effective enzymatic hydrolysis

Eucommia ulmoides Oliver (EU) wood was successively treated by autohydrolysis and organosolv pretreatment integrated process. Autohydrolysis pretreatment facilitated xylooligosaccharides production, subsequent organosolv pretreatment to obtain high-purity lignin and digestible cellulose-rich residue. Results showed that the lignin fractions obtained exhibited smaller molecular weights, narrow polydispersity, more phenolic OH groups and higher syringyl/guaiacyl ratios (S/G) than the milled wood lignin. NMR characterization of the lignin revealed that the β-O-4 linkages significantly cleaved and the structure of stilbene formed, but its resinol (β-β) was resistant to be degraded by organosolv delignification. Moreover, the glucose yield of the integrated residue achieved a maximum value of 89.3% after enzyme hydrolysis, separately about 1.0, 1.3, 3.8 times as compared to that of the ethanol organosolv residue, the hydrothermally treated residue and the EU wood, respectively, which indicated that the integrated process was a promising approach to value-added utilization of the EU wood.

Conversion of hemicellulose sugars catalyzed by formic acid: kinetics of the dehydration of D-xylose, L-arabinose, and D-glucose

The pre-treatment of lignocellulosic biomass produces a liquid stream of hemicellulose-based sugars, which can be further converted to high-value chemicals. Formosolv pulping and the Milox process use formic acid as the fractionating agent, which can be used as the catalyst for the valorisation of hemicellulose sugars to platform chemicals. The objective of this study was to investigate the reaction kinetics of major components in the hemicelluloses fraction of biomass, that is, D-xylose, L-arabinose and D-glucose. The kinetics experiments for each sugar were performed at temperatures between 130 and 170 °C in various formic acid concentrations (10-64 wt %). The implications of these kinetic models on the selectivity of each sugar to the desired products are discussed. The models were used to predict the reaction kinetics of solutions that resemble the liquid stream obtained from the fractionation process of biomass using formic acid.

Systematic evaluation of the degraded products evolved from the hydrothermal pretreatment of sweet sorghum stems

BACKGROUND

Conversion of plant cell walls to bioethanol and bio-based chemicals requires pretreatment as a necessary step to reduce recalcitrance of cell walls to enzymatic and microbial deconstruction. In this study, the sweet sorghum stems were subjected to various hydrothermal pretreatment processes (110°C to 230°C, 0.5 to 2.0 h), and the focus of this work is to systematically evaluate the degraded products of polysaccharides and lignins in the liquor phase obtained during the pretreatment process.

RESULTS

The maximum yield of xylooligosaccharides (52.25%) with a relatively low level of xylose and other degraded products was achieved at a relatively high pretreatment temperature (170°C) for a short reaction time (0.5 h). Higher temperature (>170°C) and/or longer reaction time (>0.5 h at 170°C) resulted in a decreasing yield of xylooligosaccharides, but increased the concentration of arabinose and galactose. The xylooligosaccharides obtained are composed of xylopyranosyl residues, together with lower amounts of 4-O-Me-α-D-GlcpA units. Meanwhile, the concentrations of the degraded products (especially furfural) increased as a function of pretreatment temperature and time. Molecular weights of the water-soluble polysaccharides and lignins indicated that the degradation of the polysaccharides and lignins occurred during the conditions of harsh hydrothermal pretreatment. In addition, the water-soluble polysaccharides (rich in xylan) and water-soluble lignins (rich in β-O-4 linkages) were obtained at 170°C for 1.0 h.

CONCLUSIONS

The present study demonstrated that the hydrothermal pretreatment condition had a remarkable impact on the compositions and the chemical structures of the degraded products. An extensive understanding of the degraded products from polysaccharides and lignins during the hydrothermal pretreatment will be beneficial to value-added applications of multiple chemicals in the biorefinery for bioethanol industry.

Autohydrolysis of Miscanthus x giganteus for the production of xylooligosaccharides (XOS): kinetics, characterization and recovery

The optima conditions of production and purification of xylooligosaccharides (XOS) from Miscanthus x giganteus (MxG) were investigated. Using autohydrolysis, XOS were produced at 160, 180 and 200°C at 60, 20 and 5min, respectively. XOS yield up to 13.5% (w/w) of initial biomass and 69.2% (w/w) of xylan were achieved. Results from HPAEC-PAD analysis revealed that X1-X9 sugar oligomers were produced. Higher temperature and longer reaction time resulted in lower product molecular weight. The three optimum conditions had similar degrees of polymerization XOS. Using 10% activated carbon (w/v) with ethanol/water elution recovered 47.9% (w/w) of XOS from pretreated liquid phase. The XOS could be fractionated by degree of polymerization according to ethanol concentration in the ethanol/water elution. Most of the XOS were washed out in 30% and 50% ethanol/water (v/v) fractions. Recoveries of 91.8% xylobiose, 86.9% xylotriose, 66.3% xylotetrose, 56.2% xylopentose and 48.9% xylohexaose were observed in XOS.

Kinetics of levulinic acid and furfural production from Miscanthus × giganteus

This study investigated the kinetics of acid hydrolysis of the cellulose and hemicellulose in Miscanthus to produce levulinic acid and furfural under mild temperature and high acid concentration. Experiments were carried out in an 8L-batch reactor with 9%-wt. biomass loading, acid concentrations between 0.10 and 0.53 M H2SO4, and at temperatures between 150 and 200°C. The concentrations of xylose, glucose, furfural, 5-hydroxymethylfurfural and levulinic acid were used in two mechanistic kinetic models for the prediction of the performance of ideal continuous reactors for the optimisation of levulinic acid and the concurrent production of furfural. A two-stage arrangement was found to maximise furfural in the first reactor (PFR - 185°C, 0.5M H2SO4, 27.3%-mol). A second stage leads to levulinic acid yields between 58% and 72%-mol at temperatures between 160 and 200°C.

Autohydrolysis of bamboo (Dendrocalamus giganteus Munro) culm for the production of xylo-oligosaccharides

Bamboo culm (Dendrocalamus giganteus Munro) was treated with hot water in non-isothermal conditions (140, 160, 180 and 200°C) for various reaction times (10, 30, 60 and 120 min) to generate xylo-oligosaccharides in a batch reactor at a solid to liquor ratio of 1:10 g/g. The influence of reaction conditions on yields, compositions and characteristics of the products were evaluated. The maximum yield of xylo-oligosaccharides of 47.49% was achieved at 180°C for 30 min with a relatively low level of xylose (4.73%) and other products (arabinose 0.20 g/L, galactose 0.19 g/L, HMF 0.15 g/L, furfural 0.36 g/L, acetic acid 0.64 g/L and formic acid 0.26 g/L). Higher temperature and/or longer reaction time reduced the yield of oligosaccharides, and enhanced concentrations of monosaccharides and byproducts. The result demonstrated that the yield of xylo-oligosaccharides obtained by autohydrolysis depends on the reaction temperature and time.

Degradation kinetics of the main carbohydrates in birch wood during hot water extraction in a batch reactor at elevated temperatures

Hot water extraction of wood at elevated temperatures may be a suitable method to produce hemicellulose-lean pulps and to recover xylan-derived products from the water extract. In this study, water extractions of birch wood were conducted at temperatures between 180 and 240 °C in a batch reactor. Xylan was extensively removed, whereas cellulose was partly degraded only at temperatures above 180 °C. Under severe extraction conditions, acetic acid content in the water extract was higher than the corresponding amount of acetyl groups in wood. In addition to oligo- and monosaccharides, considerable amounts of furfural and 5-hydroxymethylfurfural (HMF) were recovered from the extracts. After reaching a maximum, the furfural yield remained constant with increasing extraction time. This maximum slightly decreased with increasing extraction temperature, suggesting the preferential formation of secondary degradation products from xylose. Kinetic models fitting experimental data are proposed to explain degradation and conversion reactions of xylan and glucan.

Effect of autohydrolysis of Miscanthus x giganteus on lignin structure and organosolv delignification

The influence of the operating conditions of Miscanthus x Giganteus autohydrolysis on the composition of the solid residues and hydrolysates was examined. Milled wood lignin (MWL) extracted after autohydrolysis treatments performed at the same severity but at different temperatures were studied by (13)C and (31)P NMR in order to obtain a more complete picture of the changes in lignin structure occurring during the autohydrolysis. It was proposed that (1) the lignin homolytical fragmentation route should be enhanced with an increase of the temperature of the autohydrolysis treatment and (2) addition of a catalytic amount of 2-naphthol during the autohydrolysis step not only enhanced the dissolution of lignin but also allowed a better recovery of the hemicellulose sugars. A combined process involving an optimized autohydrolysis step (carried out in presence or not of 2-naphthol) and a low severity ethanol organosolv treatment was described for the separation and recovery of lignin, cellulose and hemicelluloses.